Had a quick look at the category_separator and I think it is not as universally usable as I would like it to be. Sometimes the answer category headers can be longer and then the format can be quite annoying:

Just an example from one of my surveys. One of the category headers is "Searching for information about..."

Well, I don't think it is complicated, but if the header is pretty long, all you will see in the text boxes is the header, and not the answer option, which can make it difficult to work on the survey. But of course, this is a minor thing.

I don't think it will be any problem for multilingual surveys. But as I usually don't use multilingual surveys, but rather create one survey per language, I am not very savvy in this area.